Europium Doped TiO(2) Hollow Nanoshells: Two-Photon Imaging of Cell Binding.

A simple scalable method to fabricate luminescent monodisperse 200 nm europium doped hollow TiO(2) nanoshell particles is reported. Fluorophore reporter, Eu(3+) ions, are incorporated directly in the NS matrix, leaving the surface free for functionalization and the core free for payload encapsulation. Amine functionalized polystyrene beads were used as templates, and the porous walls of europium doped titania nanoshells were synthesized using titanium(IV) t-butoxide and europium(III) nitrate as reactants. X-ray diffraction analysis identified anatase as the predominant titania phase of the rigid nanoshell wall structure, and photoluminescence spectra showed that the Eu(III) doped TiO(2) nanoshells exhibited a red emission at 617 nm due to an atomic f-f transition. Nanoshell interactions with HeLa cervical cancer cells in vitro were visualized using two-photon microscopy of the Eu(III) emission, and studied using a luminescence ratio analysis to assess nanoshell adhesion and endocytosis.

Controlling the role of nanopore morphology in capillary condensation.

The effect of pore morphology on capillary condensation and evaporation in nanoporous silicon is studied experimentally. A variety of cooperative and local effects are observed in tailored nanopores with well-defined regions by directly probing gas adsorption in each region using optical interferometry. All observations are ascribed to the ability of the nanopore region to access the gas reservoir directly and the nucleation of liquid bridges at local heterogeneities within the nanopore region. These assumptions, consistent with recent simulations, can be extended to any real nanoporous system.

A label-free porous alumina interferometric immunosensor.

Anodization of Al is used to produce optically smooth porous alumina (Al(2)O(3)) films with pores approximately 60 nm in diameter and approximately 6 mum deep. The capture protein, protein A, is adsorbed to the pore walls by noncovalent, electrostatic interactions, and thin film interference spectroscopy is used to detect binding of immunoglobulin (IgG). The porous alumina films are stable against corrosion and dissolution in aqueous media at pH 7, allowing quantitative monitoring of steady-state and time-resolved biomolecular binding. The bare porous Al(2)O(3) surface displays a significantly greater affinity for protein A than for IgG. The known species specificity of protein A binding to IgG is confirmed; the protein-A-modified sensor responds to IgG derived from rabbit, but not chicken (IgG/IgY). A "cascaded", or multiprobe sensing approach, is demonstrated, in which a specific target, sheep IgG, is administered to a sample modified with a protein A/rabbit anti-sheep IgG assembly. Binding measurements are confirmed by fluorescence microscopy using fluorescein-labeled IgG.

Gas adsorption and capillary condensation in nanoporous alumina films.

Gas adsorption and capillary condensation of organic vapors are studied by optical interferometry, using anodized nanoporous alumina films with controlled geometry (cylindrical pores with diameters in the range of 10-60 nm). The optical response of the film is optimized with respect to the geometric parameters of the pores, for potential performance as a gas sensor device. The average thickness of the adsorbed film at low relative pressures is not affected by the pore size. Capillary evaporation of the liquid from the nanopores occurs at the liquid-vapor equilibrium described by the classical Kelvin equation with a hemispherical meniscus. Due to the almost complete wetting, we can quantitatively describe the condensation for isopropanol using the Cohan model with a cylindrical meniscus in the Kelvin equation. This model describes the observed hysteresis and allows us to use the adsorption branch of the isotherm to calculate the pore size distribution of the sample in good agreement with independent structural measurements. The condensation for toluene lacks reproducibility due to incomplete surface wetting. This exemplifies the relevant role of the fluid-solid (van der Waals) interactions in the hysteretic behavior of capillary condensation.